Writing the MINA time server

This code should be straightforward to all. We are simply defining a main method that will be used to kick off the program. At this point, we will begin to add the code that will make up our server. First off, we need an object that will be used to listen for incoming connections. Since this program will be TCP/IP based, we will add a SocketAcceptor to our program.

As you see, there is a call to acceptor.setLocalAddress( new InetSocketAddress(PORT) );. This method defines what host and port this server will listen on. The final method is a call to IoAcceptor.bind(). This method will bind to the specified port and start processing of remote clients.

Next we add a filter to the configuration. This filter will log all information such as newly created sessions, messages received, messages sent, session closed. The next filter is a ProtocolCodecFilter. This filter will translate binary or protocol specific data into message object and vice versa. We use an existing TextLine factory because it will handle text base message for you (you don't have to write the codec part)

At this point, we will define the handler that will be used to service client connections and the requests for the current time. The handler class is a class that must implement the interface IoHandler. For almost all programs that use MINA, this becomes the workhorse of the program, as it services all incoming requests from the clients. For this tutorial, we will extend the class IoHandlerAdapter. This is a class that follows the adapter design pattern which simplifies the amount of code that needs to be written in order to satisfy the requirement of passing in a class that implements the IoHandler interface.

There are 2 new lines in the MinaTimeServer class. These methods set the set the IoHandler, input buffer size and the idle property for the sessions. The buffer size will be specified in order to tell the underlying operating system how much room to allocate for incoming data. The second line will specify when to check for idle sessions. In the call to setIdleTime, the first parameter defines what actions to check for when determining if a session is idle, the second parameter defines the length of time in seconds that must occur before a session is deemed to be idle.

The methods used in this class are exceptionCaught, messageReceived and sessionIdle. exceptionCaught should always be defined in a handler to process and exceptions that are raised in the normal course of handling remote connections. If this method is not defined, exceptions may not get properly reported.

The exceptionCaught method will simply print the stack trace of the error and close the session. For most programs, this will be standard practice unless the handler can recover from the exception condition.

The messageReceived method will receive the data from the client and write back to the client the current time. If the message received from the client is the word "quit", then the session will be closed. This method will also print out the current time to the client. Depending on the protocol codec that you use, the object (second parameter) that gets passed in to this method will be different, as well as the object that you pass in to the session.write(Object) method. If you do not specify a protocol codec, you will most likely receive a IoBuffer object, and be required to write out a IoBuffer object.

The sessionIdle method will be called once a session has remained idle for the amount of time specified in the call acceptor.getSessionConfig().setIdleTime( IdleStatus.BOTH_IDLE, 10 );.

All that is left to do is define the socket address that the server will listen on, and actually make the call that will start the server. That code is shown below:

Try out the Time server

At this point, we can go ahead and compile the program. Once you have compiled the program you can run the program in order to test out what happens. The easiest way to test the program is to start the program, and then telnet in to the program: